Sum of effects of myocardial ischemia followed by electrically induced tachycardia on myocardial function

Background: The alteration of contractile function after tachyarrhythmia ceases is influenced by the type of prior ischemia (acute coronary syndrome or ischemia inherent in a coronary revascularization procedure). We aimed to analyze cardiac dysfunction in an acute experimental model of supraphysiological heart rate preceded by different durations and types of ischemia.
Material and Methods: Twenty-four pigs were included in: (S1) series of ventricular pacing; (S2, A and B) series with 10 or 20 min, respectively, of coronary occlusion previous to ventricular pacing; S3 with 20 brief, repeated ischemia/reperfusion processes prior to ventricular pacing and; (S4) control series. Overall cardiac function parameters and regional myocardial contractility at the apex and base of the left ventricle were recorded, as were oxidative stress markers (glutathione and lipid peroxide serum levels). Left ventricular pacing at 60% over baseline heart rate was performed for 2 h followed by 1 h of recovery.
Results: High ventricular pacing rates preceded by short, repeated periods of coronary ischemia/reperfusion resulted in worse impairment of overall cardiac and regional function that continued to be altered 1 h after tachycardia ceased. There was significant reduction of stroke volume (26.9±5.3 basal vs. 16±6.2 ml; p<0.05), LVP; dP/dt and LAD flow (13.1±1.5 basal vs. 8.4±1.6 ml/min; p<0.05); the base contractility remained altered when recovering compared to baseline (base SF: 5.6±2.8 vs. 2.2±0.7%; p<0.05); and LPO levels were higher than less aggressive series at the end of recovery.
Conclusions: Ischemia and tachycardia accumulate their effects, with increased cardiac involvement depending on the type of ischemia.

Keywords: Myocardial Ischemia - physiopathology, Heart Ventricles - physiopathology, Electrophysiological Phenomena, Coronary Occlusion - physiopathology, Coronary Circulation, Cardiac Pacing, Artificial, Blood Pressure - physiology, Animals, Myocardium - pathology, Oxidative Stress, Sus scrofa, Systole - physiology, Tachycardia - physiopathology